Removal of disease such as atherosclerotic plaque, thrombus and other types of obstructions and partial obstructions from internal body lumens or cavities using advanceable, rotating operating heads is a well-established interventional technique. Numerous interventional catheters have been conceived and developed. Most of these systems require placement of a guiding catheter and guide wire prior to introduction of the interventional catheter and placement of the interventional catheter at the target operating site. Many of these prior art systems incorporate mechanical aspiration systems to remove fluid and particulates from the site, and some systems incorporate or are used in conjunction with other mechanisms such as distal filters for preventing removed material from circulating in the blood stream.
Despite the many and varied approaches to material removal systems, many challenges remain in providing systems for removing material from a lumen, such as a blood vessel, safely and reliably and without causing complications. The safety and reliability of the system is manifestly critical. Recovery of debris generated during a material removal operation, or reducing the size of the debris to a particle size that will not produce blood vessel damage or embolic events, is essential. The flexibility and size of an interventional catheter are also important features. The system must be small enough and flexible enough to navigate through sometimes tortuous internal structures and passageways, such as blood vessels, for placement at the target interventional site. The interventional catheter must also have sufficient integrity and a combination of stiffness and flexibility to operate reliably at high rotational rates while allowing for aspiration of fluids from the site and/or infusion of fluids to the site.
In interventional catheters that employ a “cutting head,” any cutter structures must be benign or retained in a protective sheath during navigation of the operating head to and from the interventional target site, yet effectively remove material during the operation. In addition, cutter structures must effectively remove disease or undesired material without damaging delicate neighboring tissue, such as blood vessel walls or other healthy tissue, which often surrounds and may be attached to the undesired material. Thus, it is important for cutter structures of interventional catheters to accurately and reliably differentiate between the diseased or undesired material and healthy tissue.
Differential cutting blades exert high shear forces against relatively hard substrates to cut or ablate relatively hard, inelastic, material. Softer, elastic structures, such as healthy tissue, blood vessel walls and the like, are deformed and displaced rather than cut by differential cutting blades, thereby reducing the shear forces and protecting elastic structures from damage. Less elastic material does not deform when contacted by a differential cutting blade, and shear stresses are consequently exerted on less elastic material to cut or scrape the material without damaging elastic tissue in proximity. In this manner, fragments of diseased, undesirable material are removed by differential cutting blades, while the more elastic, healthy tissue remains undamaged.
U.S. Pat. No. 4,445,509 describes differential cutting in the context of an atherectomy device. This patent describes a cutter assembly having a plurality of cutting flutes, each cutting flute having a blade surface operating according to the principle of differential cutting. Aspiration ports are provided in the body of the cutter assembly for collection and removal of particulates and liquids from the site of the intervention. U.S. Patent Publication 2004/0006358 A1 also discloses differential cutting surfaces forming an acute angle of attack with respect to the occlusive material. Aspiration ports are provided between the cutting surfaces.
Some interventional catheters use diamond grit on a cutting surface in an effort to provide highly divided, small particle size debris. Diamond grit particles, however, do not operate as differential cutters except in their smallest embodiment because, depending on their orientation on the cutting surface, their exposed surfaces form random cant angles producing different cutting characteristics at different points of contact with tissue. Relatively coarse diamond grit can act as a differential cutter because of the ratios of diamond size and population to tissue flexibility, but typically is more likely to damage elastic, healthy tissue such as blood vessel walls. Relatively fine diamond grit has slow material removal rates, requiring the use of higher rotational speeds. The use of grit or abrasive particles or surfaces is, however, beneficial in many applications.
The extent and consistency of the disease or undesired material forming an obstruction are frequently not well characterized prior to the intervention. Thus, although interventional catheters and cutter assemblies having different sizes and material removal properties may be provided, and may even be interchangeable on a material removal system, it is difficult to ascertain which combination of features will be most effective in any particular intervention prior to insertion of the device. Various quick-connect systems have been developed to permit removal and installation of multiple operating catheters during a single surgical intervention. Interchange, withdrawal and insertion of multiple interventional catheters, however, is time consuming, and may result in increased blood loss and increased risk to the patient.
Providing access to multiple cutter assemblies having different sizes and different material removal properties on a single interventional operating catheter is highly desirable. Interventional catheters having cutter or material removal assemblies that can be operated to vary the size of the cutting profile at the material removal site are known. Cutter assemblies comprising a distal cutter assembly having fixed blades and a proximal cutter assembly having pivoting blades are described, for example, in U.S. Pat. Nos. 6,565,588 and 6,818,001.
Several prior art interventional catheters provide for aspiration of liquids and/or debris from the material removal site. Numerous interventional catheters also provide infusion of a liquid to the site of the intervention. Infused liquids may assist in the material removal process, or may be used to deliver diagnostic, imaging or therapeutic materials prior to, during or following an intervention.
Although interventional catheters are used frequently, limitations in the flexibility, reliability and versatility, together with capability of use and performance of existing systems limit the types of disease conditions that can be effectively treated. There thus remains a need for improved interventional catheter assemblies.